I've not used DDM kits since 2007 or so. Back then, I had a lot of problems with "flicker" and stuff just not working.
Around 2010 I started using TRS products and they were AWESOME. Nothing but good things to say. Never had issues, and shipping was always stupid fast.
However, within the past year (while I have been doing retrofits for other people) I have been CONTINUOUSLY dealing with warranty issues through TRS. Multiple bulbs that manufactured incorrectly (see picture of base. That metal band is supposed to be closed, of course), ignitors not igniting (out of the box), ballasts burning out within days of use, and most recently, a wiring harness burning out.
This, along with them not allowing me to ship warrantied parts directly to the end-user, is 99% of why I stopped doing retrofits.
DSC_0260 by
Alex Wilson, on Flickr